Move aspect ratio state into PipBoundsState

Couple of changes here:
1. mAspectRatio is moved to PipBoundsState
2. Simplified getDestinationBounds by removing the aspect ratio
param. It was always re-calculated, then sent to getDestinationBounds,
then updated mAspectRatio. Now mAspectRatio is updated first and
getDestinationBounds just uses the PipBoundsState's ratio.

Bug: 169373982
Test: aspect ratio is set correctly on enter PIP, and updated during
PIP mode if app changes it (e.g. Youtube)

Change-Id: I144960ff41bde4f18eb1e9a8e60ea0cba29a8470